Gene for increasing plant weight and method for using the same

ABSTRACT

A gene having novel functions is searched for, by which plant weight (that is, biomass level) can be increased and by which substance productivity can be increased or decreased. A chimeric protein is expressed in which a transcriptional factor comprising the amino acid sequence shown in SEQ ID NO: 2, 4, or 6 is fused to a functional peptide that converts an arbitrary transcriptional factor into a transcriptional repression factor.

TECHNICAL FIELD

The present invention relates to a gene for increasing plant weight and a method for using the same.

BACKGROUND ART

The term “biomass” generally refers to the total amount of organisms that inhabit or organic matter that exists in a given area. Particularly regarding plants, plant biomass refers to the dry weight of the plants that exists in a given area. The unit of such biomass is quantified using mass or energy level. The expression “biomass is a synonym of a term “an amount of an organism.” In the case of plant biomass, the term “standing crop” is also used. Plant biomass is generated by fixing carbon dioxide in the air using solar energy, so that it can be captured as so-called carbon neutral energy. Therefore, an increase in such plant biomass has effects of terrestrial environmental protection, prevention of global warming, and reduction of greenhouse gas emissions. Hence, technologies for increasing plant biomass have high industrial importance.

In addition, plants are cultivated for their partial tissues (e.g., seeds, roots, and leaf stems) or for production of various substances such as fats and oils. For example, as fats and oils produced by plants, soybean oil, sesame oil, olive oil, coconut oil, rice oil, cottonseed oil, sunflower oil, corn oil, safflower oil, palm oil, rapeseed oil, and the like are conventionally known and broadly used for household or industrial applications. Also, fats and oils produced by plants are used as raw materials for biodiesel fuel or bioplastics, allowing the applicability thereof to spread as alternatives to petroleum as energy sources.

Under such circumstances, improvement of productivity per unit of cultivated area is required for industrially successful fat and oil production using plants. Assuming that the number of cultivated plants per unit of cultivated area remains constant, it is understood that improvement in fat and oil production per individual plant is needed. When fats and oils are collected from seeds harvested from plant bodies, it is expected that improved fat and oil production per individual plant can be achieved by a technology for improving the seed yield per individual plant, a technology for improving the fat and oil contents in seeds, or the like.

Technologies for increasing the fat and oil production from plant seeds are mainly divided into those based on improved cultivation techniques and those based on development of cultivars for increased fat and oil production. Methods for developing cultivars with increased fat and oil production are mainly divided into conventional breeding techniques mainly composed of mating technologies and molecular breeding methods using genetic recombination. As technologies for increased fat and oil production using genetic recombination, A) a technology that involves altering the synthesis system for seed triacylglycerol (TAG), which is a major ingredient of plant fats and oils, and B) a technology that involves altering various control genes for controlling plant morphological formation, metabolism, and the expression of genes involved therein are known.

Possible examples of method A) above include methods for increasing the amount of TAG synthesized using sugar produced by photosynthesis as a raw material. These include (1) a method that involves enhancing activity for the synthesis of fatty acid or glycerol, which is a component of TAG from sugar; and (2) a method for enhancing the reaction by which TAG is synthesized from glycerol and fatty acid. Concerning such methods, the following technologies have been reported as technologies using genetic engineering techniques. An example of (1) is provided in a report (Plant Physiology (1997) Vol. 11, pp. 75-81) wherein it was noted that seed fat and oil contents were improved by 5% via overexpression of cytoplasmic acetyl-coenzyme A carboxylase (ACCase) of Arabidopsis thaliana in rapeseed plastids. Also, an example of (2) is provided in a report (Plant Physiology (2001), Vol. 126, pp. 861-874) concerning a technology for increased fat and oil production via overexpression of DGAT (diacylglycerol acyltransferase), which undergoes acyl transfer to the sn-3 position of diacylglycerol. In the report regarding this method, fat and oil contents and seed weights were increased as the DGAT expression levels were increased, so that the number of seeds per individual plant could increase. Arabidopsis thaliana seed fat and oil content was increased by 46% with the use of this method, and the fat and oil content per individual plant was increased by approximately 125% at maximum.

In addition, a possible example of method B) above is a method that involves controlling the expression of a transcriptional factor gene involved in control of the expression of a biosynthesis system enzyme gene. An example thereof is given in WO01/36597. In WO01/36597, a technique was employed that involves producing recombinant plants through exhaustive overexpression or knock-out of a transcriptional factor and then selecting a gene that enhances seed fat and oil contents. WO01/36597 states that seed fat and oil contents were increased by 23% through overexpression of the ERF subfamily B-4 transcriptional factor gene. However, WO01/36597 does not state increases or decreases in the fat and oil content per individual plant. Plant J. (2004) 40, 575-585 describes that seed fat and oil contents can be improved by overexpression of WRINKLED1, the transcriptional factor containing the AP2/EREB domain.

Furthermore, when a hydrocarbon component such as cellulose contained in plant bodies is glycosylated and then alcohol is produced by fermentation, fat and oil components contained in plants become impurities that can cause reduced glycosylation efficiency in a glycosylation step. Therefore, if fat and oil contents can be decreased, glycosylation efficiency in a glycosylation step can be improved and thus improved alcohol productivity can be expected. For example, Plant J. (2004) 40, 575-585 discloses that in the case of the WRI1/ASML1 (AP2 family transcriptional factor: AGI-code; AT3g54320)-deficient line, seeds were wrinkled and the fat and oil contents were decreased. Furthermore, WO01/35727 discloses the following: the seed fat and oil content was decreased by 13% through overexpression of AT3g23250 (MYB15); the seed fat and oil content was decreased by 12% through overexpression of AT1g04550 (IAA12); and the seed fat and oil content was decreased by 16% through overexpression of AT1g66390 (MYB90).

Moreover, several attempts to improve biomass have been carried out. For example, Proc. Natl. Acad. Sci. U.S.A., 2000, Jan. 18; 97(2), 942-947 discloses that plant organ cell number, organ size, and individual plant size were increased through overexpression of the At4g37750 (AINTEGUMENTA) gene. Similarly, Plant Cell, 2003, Sep.; 15(9), 1951-1961 discloses that when overexpression of At2g44080 (ARL) was caused, plant organ cell number, organ size, and individual plant size were increased. Also, Plant J. (2006) July, 47(1), 1-9 discloses that cell division was activated through overexpression of At1g15690 (AVP1), so that individual plant size was increased. Furthermore, Development 2006, January; 133 (2), 251-261 reports that when At5g62000 (ARF2) was deficient, seeds and flower organs became larger in size.

However, although the above molecular breeding methods for improvement of various characters have been developed, no technology has reached a practical level that would allow both increased biomass and improved or decreased fat and oil productivity.

This may be because truly excellent genes remain undiscovered and because novel recombinant cultivars effective at test stages are unable to exert effects as desired at practical stages under various natural environments. Furthermore, regarding quantitative character such as increased plant weight and productivity of a target substance, many genes are involved in various steps, ranging from control systems to metabolic systems. Hence, it has been difficult to discover and develop a truly excellent useful gene for improvement of quantitative characters. Objects required to address these problems are: discovery of a novel gene with drastically high effects; and development of a gene capable of exerting effects under practical environmental conditions, even if its effect levels are equivalent to those of conventional genes. Furthermore, it is expected that practical levels would be achieved by the simultaneous use of a plural number of genes, even if each of the genes has effect level equivalent to or lower than those of conventional genes. Accordingly, another object is to develop a plurality of genes having different functions.

DISCLOSURE OF THE INVENTION Object to be Achieved by the Invention

In view of the above-described circumstances, an object of the invention is to search for a gene having novel functions by which plant weight (that is, plant biomass level) can be increased and by means of which substance productivity can be increased or decreased, so as to provide a technology capable of improving the properties of plant bodies.

Means to Achieve the Object

As a result of intensive studies to achieve the above objects, the present inventors have discovered that various quantitative characters can be improved through expression of a chimeric protein in which a specific transcriptional factor is fused to a functional peptide (hereinafter, this may also be referred to as a repressor domain) that converts an arbitrary transcriptional factor to a transcriptional repression factor. Particularly, the present inventors have discovered that plant weight (that is, plant biomass level) can be increased and that substance productivity can be increased or decreased. Thus, the present inventors have completed the present invention.

The plant body according to the present invention expresses a chimeric protein wherein a transcriptional factor comprising any one of the following proteins (a) to (c) is fused to a functional peptide that converts an arbitrary transcriptional factor to a transcriptional repression factor:

(a) a protein comprising the amino acid sequence shown in SEQ ID NO: 2, 4, or 6;

(b) a protein comprising an amino acid sequence that has a deletion, a substitution, an addition, or an insertion of one or a plurality of amino acids with respect to the amino acid sequence shown in SEQ ID NO: 2, 4 or 6 and having activity of accelerating transcription; and

(c) a protein encoded by a polynucleotide hybridizing under stringent conditions to a polynucleotide that comprises a nucleotide sequence complementary to the nucleotide sequence shown in SEQ ID NO: 1, 3, or 5 and having activity of accelerating transcription.

In the plant body according to the present invention, the transcriptional control activity and particularly the activity of accelerating transcription of a predetermined transcriptional factor is preferably suppressed by fusion of a functional peptide. Examples of the above functional peptide include the peptides represented by the following formulae (1) to (8), respectively: X1-Leu-Asp-Leu-X2-Leu-X3 (SEQ ID NO: 14 with deletion of 0-10 residues from the N-terminus)  (1) (wherein X1 denotes 0 to 10 amino acid residues, X2 denotes Asn or Glu, and X3 denotes at least 6 amino acid residues.) Y1-Phe-Asp-Leu-Asn-Y2-Y3 (SEQ ID NO: 15 with deletion of 0-10 residues from the N-terminus)  (2) (wherein Y1 denotes 0 to 10 amino acid residues, Y2 denotes Phe or Ile, and Y3 denotes at least 6 amino acid residues.) Z1-Asp-Leu-Z2-Leu-Arg-Leu-Z3 (SEQ ID NO: 16 with deletion of 0-10 residues from the C-terminus and deletion of 0-2 residues from the N-terminus)  (3) (wherein Z1 denotes Leu, Asp-Leu, or Leu-Asp-Leu, Z2 denotes Glu, Gln, or Asp, and Z3 denotes 0 to 10 amino acid residues.) Asp-Leu-Z4-Leu-Arg-Leu (SEQ ID NO: 17)  (4) (wherein Z4 denotes Glu, Gln, or Asp.) alpha1-Leu-beta1-Leu-gamma1-Leu (SEQ ID NO: 18)  (5) alpha1-Leu-beta1-Leu-gamma2-Leu (SEQ ID NO: 19)  (6) alpha1-Leu-beta2-Leu-Arg-Leu (SEQ ID NO: 20)  (7) alpha2-Leu-beta1-Leu-Arg-Leu (SEQ ID NO: 21);  (8) (and in the formulae (5) to (8), alpha1 denotes Asp, Asn, Glu, Gln, Thr, or Ser, alpha2 denotes Asn, Glu, Gln, Thr, or Ser, beta1 denotes Asp, Gln, Asn, Arg, Glu, Thr, Ser, or His, beta2 denotes Asn, Arg, Thr, Ser, or His, gamma1 denotes Arg, Gln, Asn, Thr, Ser, His, Lys, or Asp, and gamma2 denotes Gln, Asn, Thr, Ser, His, Lys, or Asp.) The plant weight of the plant body according to the present invention is significantly improved. Here, the term “significantly” refers to a situation in which the plant weight is increased to a statistically significant extent compared with the plant weight of a plant body not expressing the above chimeric protein.

Also, in the plant body according to the present invention, substance productivity per individual plant, and particularly, the productivity of fats and oils contained in seeds, is significantly improved or decreased. Examples of specific tissues include seeds. Here, the term “significantly” refers to a situation in which substance productivity is increased or decreased to a statistically significant extent compared with substance productivity in a plant body not expressing the above chimeric protein.

Meanwhile, according to the present invention, the above-described chimeric protein, a gene encoding the chimeric protein, an expression vector containing the gene, and a transformant containing the gene can be provided.

Effect of the Invention

The plant body according to the present invention has improved plant weight; that is, it exhibits an improved biomass level. Therefore, by the use of the plant body according to the present invention, improvement can be achieved in terms of productivity of a substance that is produced using a plant body itself or a part of a plant body as a raw material, such as bioalcohol. Thus, a substance of interest can be produced at low cost according to the present invention.

BEST MODE OF CARRYING OUT THE INVENTION

The present invention will be described in detail as follows.

The plant body according to the present invention expresses a chimeric protein in which a predetermined transcriptional factor is fused to a functional peptide that converts an arbitrary transcriptional factor to a transcriptional repression factor and has a significantly improved plant weight (that is, a plant biomass level) compared with that of wild-type plant bodies. Specifically, the plant body according to the present invention is produced by causing a desired (target) plant to express a transcriptional factor in the form of a chimeric protein with the above functional peptide, so as to significantly improve the plant biomass level of the plant. Also, the plant body of the present invention has significantly improved or decreased substance productivity per individual plant and particularly improved productivity of fats and oils contained in seeds, compared with wild-type plant bodies.

In particular, it is preferable that, in the plant body according to the present invention, the activity of accelerating transcription of the transcriptional factor is suppressed through fusion of the factor with the above functional peptide. That is, preferably, the plant body according to the present invention is characterized in that, as a result of expression of a chimeric protein in which the above functional peptide is fused to a transcriptional factor, the transcriptional repression effect resulting from the above functional peptide appears as a dominant character.

Here, the expression, “improvement of the plant weight” is synonymous with namely, “increased biomass,” that is; increased biomass per given area. Two technologies contribute to increase the biomass per given area: a technology for increasing the degree of dense planting (the number of plants per given area) and a technology for increasing the weight or energy level per individual plant. Hence, not only the dry weight per given area, but also the dry weight per individual plant can also be evaluated as plant biomass.

Accordingly, the biomass as defined in the present invention may be dry plant weight per individual plant, the dry weight (per individual plant) of the above ground part of a plant, or the weight of a specific tissue. Here, the term “tissue weight per individual plant” refers to the weight of at least one or more types of tissue selected from among seeds, roots, leaves, stems, flowers, pollens, and the like, composing a plant.

The term “substance productivity per individual plant” refers to the content per unit volume of one of various substances generated by plants. A substance to be used herein is not particularly limited and may be a substance that is originally generated by a plant body or a substance that is not originally generated by a plant body but can be generated by the plant body as a result of genetic engineering, or the like.

Particularly, if the content of a product of interest per tissue is increased, the present invention is industrially useful, since purification cost and transportation cost can be reduced. Particularly, a product of interest may be lignocellulose the weight of which accounts for most weight of the plant or plant oil that is industrially used as seed oil. Plant oil may be simple lipid that is an ester of fatty acid and alcohol, complex lipid containing phosphorus, sugar, nitrogen, and the like, or fatty acid itself. Alcohol of simple lipid may be high-molecular-weight higher alcohol or polyalcohol such as glycerol (glycerine). Fatty acid of simple lipid may be saturated fatty acid or unsaturated fatty acid, as well as, special fatty acid containing a hydroxyl group and an epoxy group. Simple lipid that is an ester of glycerol and fatty acid may be monoacylglycerol, diacylglycerol, or triacylglycerol.

Meanwhile, depending on the application of a plant body, a predetermined substance contained in the plant body may be an impurity. Therefore, the lower the productivity of a predetermined substance, the more decreased impurity content, leading to high industrial usefulness. For example, when lignocellulose contained in a plant body is glycosylated, a fat and oil component contained in the plant body as an impurity may adversely affect glycosylation efficiency. Hence, if the productivity of fats and oils is decreased, the efficiency of a glycosylation step of the production process for bioalcohol or the like using plant bodies can be improved.

The following explanation is given by exemplifying fats and oils as substances that improve or decrease productivity, but the technical scope of the present invention is not limited thereto. The present invention is similarly applicable to substances to be generated by plants other than fats and oils.

The plant body to be used herein is not particularly limited. Any plant can be a target. Particularly preferably such target plants are those conventionally used for production of fats and oils. Examples of such target plants include soybean, sesame, olive oil, coconut, rice, cotton, sunflower, corn, sugarcane, jatropha, palm coconut, tobacco, safflower, and rapeseed. Also, another possible target plant is Arabidopsis thaliana that has been broadly used as a model organism for plant gene analysis, for which a method for gene expression analysis has been established.

Also, the transcriptional repression is the activity of a chimeric protein comprising a transcriptional factor, by which a cis sequence to be recognized by the transcriptional factor or a cis sequence analogous thereto in another transcriptional factor is recognized, so as to aggressively suppress downstream gene expression. Transcriptional repression can also be referred to as a transcriptional repression factor. A technique for undergoing transcriptional repression possessed as activity by a chimeric protein comprising a transcriptional factor is not particularly limited. Particularly, a method for constructing a chimeric protein (fusion protein) to which a repressor domain sequence or an SRDX sequence has been added is most preferable.

A repressor domain sequence in this technique is an amino acid sequence composing a peptide that converts an arbitrary transcriptional factor to a transcriptional repression factor and the present inventors have discovered various types thereof. Regarding methods using repressor domain sequences, JP Patent Publication (Kokai) No. 2001-269177 A, JP Patent Publication (Kokai) No. 2001-269178 A, JP Patent Publication (Kokai) No. 2001-292776 A, JP Patent Publication (Kokai) No. 2001-292777 A, JP Patent Publication (Kokai) No. 2001-269176 A, JP Patent Publication (Kokai) No. 2001-269179 A, International Patent Publication WO03/055903, Pamphlet, Ohta, M., Matsui, K., Hiratsu, K., Shinshi, H. and Ohme-Takagi, M., The Plant Cell, Vol. 13, 1959-1968, August, 2001, and Hiratsu, K., Ohta, M., Matsui, K., Ohme-Takagi, M., FEBS Letters 514 (2002) 351-354 can be referred to, for example. A repressor domain sequence is excised from Class II ERF (Ethylene Responsive Element Binding Factor) protein or a plant zinc finger protein (e.g., Arabidopsis thaliana SUPERMAN protein) and has an extremely simple structure.

Examples of a transcriptional factor that is expressed in the form of a chimeric protein include a transcriptional factor (hereinafter, simply referred as the “transcriptional factor At3g04070.” The same applies to the following examples) specified under AG1 code At3g04070 of Arabidopsis thaliana, the transcriptional factor At1g18330, and the transcriptional factor At3g45150. In addition, the transcriptional factor At3g04070 is a transcriptional factor belonging to the NAC family. The transcriptional factor At1g18330 is a transcriptional factor belonging to the single MYB (R3-MYB) family. The transcriptional factor At3g45150 is a transcriptional factor belonging to the TCP family. The amino acid sequence of the transcriptional factor At3g04070 is shown in SEQ ID NO: 2 and the nucleotide sequence of a gene encoding the transcriptional factor At3g04070 is shown in SEQ ID NO: 1. The amino acid sequence of the transcriptional factor At1g18330 is shown in SEQ ID NO: 4 and the nucleotide sequence of a gene encoding the transcriptional factor At1g18330 is shown in SEQ ID NO: 3. The amino acid sequence of the transcriptional factor At3g45150 is shown in SEQ ID NO: 6 and the nucleotide sequence of a gene encoding the transcriptional factor At3g45150 is shown in SEQ ID NO: 5.

Moreover, the transcriptional factor At3g04070, the transcriptional factor At1g18330, and the transcriptional factor At3g45150 that are targets of a chimeric protein are not limited to those comprising amino acid sequences shown in SEQ ID NOS: 2, 4, and 6, respectively. Such a target transcriptional factor may comprise an amino acid sequence that has a deletion, a substitution, an addition, or an insertion of one or a plurality of amino acids with respect to the amino acid sequence shown in SEQ ID NO: 2, 4, or 6 and having activity of accelerating transcription. Here the term “a plurality of amino acids” refers to 1 to 20, preferably 1 to 10, more preferably 1 to 7, further more preferably 1 to 5, and particularly preferably 1 to 3 amino acids, for example. In addition, a deletion, a substitution, or an addition of amino acids can be performed by altering a nucleotide sequence encoding the above transcriptional factor by techniques known in the art. A mutation can be introduced into a nucleotide sequence by a known technique such as the Kunkel method or the Gapped duplex method or a method according thereto. For example, a mutation is introduced using a mutagenesis kit using site-directed mutagenesis (e.g., Mutant-K and Mutant-G (both of which are trade names, manufactured by TAKARA Bio)) or using a LA PCR in vitro Mutagenesis series kit (trade name, manufactured by TAKARA Bio). Also, a mutagenesis method may be a method that uses a chemical agent for mutation represented by EMS (ethylmethane sulfonate), 5-bromouracil, 2-aminopurine, hydroxylamine, N-methyl-N′-nitro-N-nitrosoguanidine, or other carcinogenic compounds or a method based on radiation treatment typically using an X ray, an alpha ray, a beta ray, a gamma-ray, or an ion beam or ultraviolet {UV} treatment.

Furthermore, examples of a transcriptional factor that is a target of a chimeric protein are not limited to the transcriptional factor At3g04070, the transcriptional factor At1g18330, and the transcriptional factor At3g45150 of Arabidopsis thaliana. Examples thereof also include transcriptional factors (hereinafter, referred as homologous transcriptional factors) having the same functions in plants (e.g., the above-mentioned plants) other than Arabidopsis thaliana. Transcriptional factors homologous to the transcriptional factor At3g04070, the transcriptional factor At1g18330, and the transcriptional factor At3g45150 can be searched for from plant genome information to be searched based on the amino acid sequence of the transcriptional factor At3g04070, the transcriptional factor At1g18330, or the transcriptional factor At3g45150 or the nucleotide sequence of each gene thereof, as long as the plant genome information has been revealed. At this time, a homologous transcriptional factor is searched for as an amino acid sequence having 70% or more, preferably 80% or more, more preferably 90% or more, and most preferably 95% or more homology with respect to the amino acid sequence of the transcriptional factor At3g04070, the transcriptional factor At1g18330, or the transcriptional factor At3g45150. Here, the value of homology refers to a value found using database that store a computer program mounting blast algorithm, gene sequence information, and default setting.

Moreover, when plant genome information is unknown, a homologous gene can be identified by extracting a genome from a target plant or constructing a cDNA library of a target plant, and then isolating a genomic region or cDNA hybridizing under stringent conditions to at least a part of a gene encoding the transcriptional factor At3g04070, the transcriptional factor At1g18330, or the transcriptional factor At3g45150. Here, the term “stringent conditions” refers to conditions where a so-called specific hybrid is formed, but no non-specific hybrid is formed. For example, hybridization is performed at 45 degrees C. using 6×SSC (sodium chloride/sodium citrate) and then washing is performed under conditions of 50 degrees C.-65 degrees C., 0.2-1×SSC, and 0.1% SDS. Alternatively, examples thereof include hybridization at 65 degrees C.-70 degrees C. using 1×SSC followed by washing at 65 degrees C.-70 degrees C. using 0.3×SSC. Hybridization can be performed by a conventionally known method such as a method described in J. Sambrook et al. Molecular Cloning, A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory (1989).

The plant body according to the present invention is characterized in that as a result of expression of the above-described chimeric protein of a transcriptional factor and a functional peptide, the plant weight (that is, a biomass level) is significantly improved, and that fat and oil production is significantly changed (improved or decreased). Particularly, the plant body according to the present invention is characterized in that, through preparation of such a chimeric protein, a target transcriptional factor is expressed in the form of the chimeric protein with suppressed activity of accelerating transcription, and transcriptional repression activity is expressed to recognize a cis sequence having homology with a cis sequence that is recognized by the target transcriptional factor. Furthermore, the plant body is also characterized in that the plant weight (that is, biomass level) is significantly improved, and that fat and oil production is significantly changed (improved or decreased) by varying the affinity specificity of the target transcriptional factor for another factor, nucleic acid, lipid, or carbohydrate. At this time, in the above plant body, a chimeric protein may be prepared via alteration of an endogenous transcriptional factor or a gene encoding a chimeric protein may be introduced and then the gene is expressed.

As an example, a preferable technique involves introducing a gene encoding a chimeric protein (fusion protein) in which the above-described transcriptional factor is fused to a functional peptide that converts an arbitrary transcriptional factor to a transcriptional repression factor into a target plant and then causing expression of the chimeric protein (fusion protein) within the plant.

The term “transcriptional factor with suppressed activity of accelerating transcription” described in this Description is not particularly limited and refers to a transcriptional factor having significantly decreased activity of accelerating transcription that is originally possessed by the transcriptional factor. Also, the term “functional peptide that converts an arbitrary transcriptional factor to a transcriptional repression factor” refers to, when it is fused to an arbitrary transcriptional factor to form a chimeric protein, a peptide that has functions so that the resulting transcriptional factor has significantly decreased activity of accelerating transcription that is originally possessed by the transcriptional factor (it may also be referred to as a transcriptional repression conversion peptide). Such “a functional peptide that converts an arbitrary transcriptional factor to a transcriptional repression factor” is not particularly limited, but is preferably a peptide comprising an amino acid sequence known as particularly a repressor domain sequence or an SRDX sequence. Such transcriptional repression conversion peptide is described in detail in JP Patent Publication (Kokai) No. 2005-204657 A and all peptides disclosed in this publication can be used herein.

Examples of the transcriptional repression conversion peptide include the peptides of the amino acid sequences represented by the following formulae (1) to (8), respectively. X1-Leu-Asp-Leu-X2-Leu-X3 (SEQ ID NO: 14 with deletion of 0-10 residues from the N-terminus)  (1) (wherein X1 denotes 0 to 10 amino acid residues, X2 denotes Asn or Glu, and X3 denotes at least 6 amino acid residues) Y1-Phe-Asp-Leu-Asn-Y2-Y3 (SEQ ID NO: 15 with deletion of 0-10 residues from the N-terminus)  (2) (wherein Y1 denotes 0 to 10 amino acid residues, Y2 denotes Phe or Ile, and Y3 denotes at least 6 amino acid residues) Z1-Asp-Leu-Z2-Leu-Arg-Leu-Z3 (SEQ ID NO: 16 with deletion of 0-10 residues from the C-terminus and deletion of 0-2 residues from the N-terminus)  (3) (wherein Z1 denotes Leu, Asp-Leu, or Leu-Asp-Leu, Z2 denotes Glu, Gln, or Asp, and Z3 denotes 0 to 10 amino acid residues) Asp-Leu-Z4-Leu-Arg-Leu (SEQ ID NO: 17)  (4) (wherein Z4 denotes Glu, Gln, or Asp) alpha1-Leu-beta1-Leu-gamma1-Leu (SEQ ID NO: 18)  (5) alpha1-Leu-beta1-Leu-gamma2-Leu (SEQ ID NO: 19)  (6) alpha1-Leu-beta2-Leu-Arg-Leu (SEQ ID NO: 20)  (7) alpha2-Leu-beta1-Leu-Arg-Leu (SEQ ID NO: 21);  (8) (and in the formulae (5) to (8), alpha1 denotes Asp, Asn, Glu, Gln, Thr, or Ser, alpha2 denotes Asn, Glu, Gln, Thr, or Ser, beta1 denotes Asp, Gln, Asn, Arg, Glu, Thr, Ser, or His, beta2 denotes Asn, Arg, Thr, Ser, or His, gamma1 denotes Arg, Gln, Asn, Thr, Ser, His, Lys, or Asp, and gamma2 denotes Gln, Asn, Thr, Ser, His, Lys, or Asp) Transcriptional Repression Conversion Peptide of Formula (1)

In the transcriptional repression conversion peptide of the above formula (1), the number of amino acid residues denoted by X1 above may range from 0 to 10. Also, the specific types of amino acid composing the amino acid residues denoted by X1 are not particularly limited, and they may be of any type. The amino acid residues denoted by X1 are preferably as short as possible, in view of ease of synthesis of the transcriptional repression conversion peptide of formula (1). The number of amino acid residues that are specifically denoted by X1 is preferably 5 or less.

Similarly, in the case of the transcriptional repression conversion peptide of formula (1), the number of amino acid residues denoted by X3 above may be at least 6. Also, the specific types of amino acid composing amino acid residues denoted by X3 are not particularly limited, and they may be of any type.

Transcriptional Repression Conversion Peptide of Formula (2)

In the transcriptional repression conversion peptide of formula (2) above, similarly to the case of X1 of the transcriptional repression conversion peptide of formula (1) above, the number of amino acid residues denoted by Y1 above may range from 0 to 10. Also, the specific types of amino acid composing the amino acid residues denoted by Y1 are not particularly limited, and they may be of any type. The specific number of amino acid residues denoted by Y1 is preferably 5 or less.

In the transcriptional repression conversion peptide of formula (2) above, similarly to the case of X3 of the transcriptional repression conversion peptide of formula (1) above, the number of amino acid residues denoted by Y3 above may be at least 6. Also, the specific types of amino acid composing the amino acid residues denoted by Y3 are not particularly limited, and they may be of any type.

Transcriptional Repression Conversion Peptide of Formula (3)

In the transcriptional repression conversion peptide of formula (3) above, the amino acid residues denoted by Z1 above includes 1 to 3 Leu residues. When the number of amino acids is 1, the amino acid is Leu. When the number of amino acids is 2, they are Asp-Leu. When the number of amino acids is 3, they are Leu-Asp-Leu.

Meanwhile, in the transcriptional repression conversion peptide of formula (3) above, the number of amino acid residues denoted by Z3 above may range from 0 to 10. Also, the specific types of amino acid composing amino acid residues denoted by Z3 are not particularly limited, and they may be of any type, Specifically, the number of amino acid residues denoted by Z3 is more preferably 5 or less. Specific examples of amino acid residues denoted by Z3 include, but are not limited to, Gly, Gly-Phe-Phe, Gly-Phe-Ala, Gly-Tyr-Tyr, and Ala-Ala-Ala.

Moreover, the total number of amino acid residues in the transcriptional repression conversion peptide represented by formula (3) is not particularly limited. In view of the ease upon synthesis, the number thereof is preferably 20 amino acids or less.

Transcriptional Repression Conversion Peptide of Formula (4)

The transcriptional repression conversion peptide of formula (4) is a hexamer (6 mer) consisting of 6 amino acid residues. In addition, when the amino acid residue denoted by Z4 in the transcriptional repression conversion peptide of formula (4) above is Glu, the amino acid sequence corresponds to a sequence ranging from amino acid 196 to amino acid 201 of Arabidopsis thaliana SUPERMAN protein (SUP protein).

Various transcriptional repression conversion peptides explained above can alter the properties of the above described transcriptional factor by fusion thereof to the transcriptional factor, so as to form a chimeric protein (fusion protein). Specifically, through fusion to the above described transcriptional factor so as to form a chimeric protein (fusion protein), such peptide can alter the relevant transcriptional factor to a transcriptional repression factor or a negative transcription coupling factor. Furthermore, such peptide can also convert a transcriptional repression factor that is not dominant to a dominant transcriptional repression factor.

A chimeric protein (fusion protein) can also be produced by obtaining a fusion gene using a polynucleotide encoding the above transcriptional repression conversion peptide and a gene encoding a transcriptional factor. Specifically, a fusion gene is constructed by linking a polynucleotide (referred to as transcriptional repression conversion polynucleotide) encoding the above transcriptional repression conversion peptide and a gene encoding the above transcriptional factor and then introduced into plant cells, so that a chimeric protein (fusion protein) can be produced by the cells. A specific example of the nucleotide sequence of the above transcriptional repression conversion polynucleotide is not particularly limited, as long as it is based on genetic codes and contains a nucleotide sequence corresponding to the amino acid sequence of the above transcriptional repression conversion peptide. Also, if necessary, the above transcriptional repression conversion polynucleotide may further contain a nucleotide sequence that serves as a joining site for linking with a transcriptional factor gene. Furthermore, when the amino acid reading frame of the above transcriptional repression conversion polynucleotide does not agree with the reading frame of a transcriptional factor gene, such polynucleotide may contain an additional nucleotide sequence for their agreement. Furthermore, such polynucleotide may also contain various additional polypeptides such as a polypeptide having a linker function for linking a transcriptional factor and a transcriptional repression conversion peptide and polypeptides (e.g., His, Myc, or Flag) for epitope labeling of the chimeric protein (fusion protein). Furthermore, the above chimeric protein (fusion protein) may contain structures other than polypeptides, if necessary, such as a sugar chain and an isoprenoid group.

A method for producing plant bodies is not particularly limited, as long as it comprises a process for production of the above-described chimeric protein of a transcriptional factor and a transcriptional repression conversion peptide in plant bodies. An example thereof is a production method comprising the steps of constructing an expression vector, transformation, selection, and the like. Each step is specifically explained as follows.

Step of Constructing Expression Vector

The step of constructing an expression vector is not particularly limited, as long as it is a step of constructing a recombinant expression vector containing a gene encoding the above transcriptional factor, a transcriptional repression conversion polynucleotide, and a promoter. As a vector to be used as a template for a recombinant expression vector, various conventionally known vectors can be used. For example, plasmids, phages, or cosmids can be used. A vector can be appropriately selected therefrom depending on a plant cell into which the vector is introduced or a method employed for introduction. Specific examples thereof include pBR322, pBR325, pUC19, pUC119, pBluescript, pBluescriptSK, and pBI vectors. Particularly, when a method for introducing a vector into a plant body is a method using Agrobacterium, a pBI binary vector is preferably used. Specific examples of such pBI binary vector include pBIG, pBIN19, pBI101, pBI121, and pBI221.

A promoter to be used herein is not particularly limited, as long as it enables gene expression within a plant body. A known promoter can be preferably used. Examples of such promoter include a cauliflower mosaic virus 35S promoter (CaMV35S), various actin gene promoters, various ubiquitin gene promoters, a promoter of a nopaline synthase gene, a tobacco PR1a gene promoter, a tomato ribulose 1,5-bisphosphate carboxylase oxidase small subunit gene promoter, a napin gene promoter, and an oleosin gene promoter. Of these promoters, a cauliflower mosaic virus 35S promoter, actin gene promoters, or ubiquitin gene promoters can be more preferably used. The use of each of the above promoters enables strong expression of an arbitrary gene after its introduction into plant cells. A promoter is ligated to and introduced into a vector, so that a fusion gene can be expressed in which a gene encoding a transcriptional factor or a transcription coupling factor is linked to a transcriptional repression conversion polynucleotide. The specific structure of a recombinant expression vector is not particularly limited.

In addition, a recombinant expression vector may further contain other DNA segments in addition to a promoter and the above fusion gene. Examples of such other DNA segments are not particularly limited and include a terminator, a selection marker, an enhancer, and a nucleotide sequence for enhancing translation efficiency. Also, the above recombinant expression vector may further has a T-DNA region. A T-DNA region can enhance gene transfer efficiency particularly when the above recombinant expression vector is introduced into plant bodies using Agrobacterium.

A transcriptional terminator to be used herein is not particularly limited, as long as it has functions as a transcription termination site and may be a known transcriptional terminator. For example, specifically, a transcription termination region (Nos terminator) of a nopaline synthase gene, a transcription termination region (CaMV35S terminator) of cauliflower mosaic virus 35S, and the like can be preferably used. Of these examples, the Nos terminator can be more preferably used. In the above recombinant vector, a transcriptional terminator is placed at an appropriate position, so as to be able to prevent the occurrence of phenomena such as the synthesis of unnecessarily long transcripts and reduced number of copies of a plasmid because of a strong promoter, after introduction into plant cells.

As a transformant selection marker, a drug resistance gene can be used, for example. A specific example of such drug resistance gene is a drug resistance gene against hygromycin, bleomycin, kanamycin, gentamicin, chloramphenicol, or the like. Hence, transformed plant bodies can be easily selected through selection of plant bodies that can grow in medium containing the above antibiotic.

An example of a nucleotide sequence for enhancing translation efficiency is a tobacco mosaic virus-derived omega sequence. The omega sequence is placed in the untranslated region (5′ UTR) of a promoter, allowing the translation efficiency of the above fusion gene to be enhanced. As described above, the above recombinant expression vector can contain various DNA segments depending on purpose.

A method for constructing a recombinant expression vector is not particularly limited. The above promoter, a gene encoding a transcriptional factor, and a transcriptional repression conversion polynucleotide, as well as (if necessary) the above other DNA segments are introduced in a predetermined order into a vector appropriately selected as a template. For example, a fusion gene is constructed by linking a gene encoding a transcriptional factor and a transcriptional repression conversion polynucleotide. Next the fusion gene and a promoter (and if necessary, a transcriptional terminator and the like) are linked to construct an expression cassette and then the expression cassette is introduced into a vector.

Upon construction of a chimeric gene (fusion gene) and that of an expression cassette, for example, cleavage sites of DNA segments are treated to have protruding ends complementary from each other. Reaction is performed using a ligation enzyme, making it possible to determine the order of the DNA segments. In addition, when an expression cassette contains a terminator, from upstream, a promoter, the above chimeric gene, and a terminator should be placed in this order. Also, reagents for construction of a recombinant expression vector; that is, the types of restriction enzyme and ligation enzyme, for example, are also not particularly limited. Commercially available reagents may be appropriately selected and then used.

Moreover, a method for proliferating the above recombinant expression vector (production method) is also not particularly limited. Conventionally known methods can be used herein. In general, such vector may be proliferated within Escherichia coli as a host. At this time, a preferred type of Escherichia coli may be selected depending on the type of a vector.

Transformation Step

A transformation step that is performed in the present invention is a step of introducing the above fusion gene into plant cells using the above recombinant expression vector, so that the fusion gene is expressed. A method for introducing such gene into plant cells using a recombinant expression vector (transformation method) is not particularly limited. Any appropriate conventionally known method can be employed depending on plant cells. Specifically, for example, a method that uses Agrobacterium or a method that involves directly introducing such gene into plant cells can be employed herein. As such method that uses Agrobacterium, for example, a method described in Bechtold, E., Ellis, J. and Pelletier, G. (1993) In Planta Agrobacterium-mediated gene transfer by infiltration of adult Arabidopsis plants. C. R. Acad. Sci. Paris Sci. Vie, 316, 1194-1199, or a method described in Zyprian E, Kado Cl, Agrobacterium-mediated plant transformation by novel mini-T vectors in conjunction with a high-copy vir region helper plasmid. Plant Molecular Biology, 1990, 15(2), 245-256, can be employed.

As a method that involves direct introduction of DNA containing a recombinant expression vector and a target gene, into plant cells microinjection, electroporation, a polyethylene glycol method, a particle gun method, protoplast fusion, a calcium phosphate method, or the like can be employed.

Also, when a method that involves direct introduction of DNA into plant cells is employed, DNA to be used herein contains at least transcriptional units that are required for the expression of a target gene such as a promoter and a transcriptional terminator, and the target gene. Vector functions are not essential herein. Furthermore, even if DNA contains only the protein coding region of a target gene having no transcriptional unit, such DNA can also be used herein, as long as it can be integrated into a host transcriptional unit and the target gene can be expressed.

Examples of plant cells, into which DNA containing the above recombinant expression vector and a target gene or DNA containing only target gene DNA without containing any expression vector is introduced, include cells of each tissue in plant organs such as flowers, leaves, and roots, calli, and suspension-cultured cells. In a method for producing the plant body according to the present invention, as the above recombinant expression vector, an appropriate vector may be adequately constructed depending on the type of a plant body to be produced. Alternatively, a versatile recombinant expression vector is constructed in advance and then the vector may be introduced into plant cells. Specifically, the method for producing the plant body according to the present invention may or may not comprise a step of constructing DNA for transformation using the above recombinant expression vector.

Other Steps and Methods

A method for producing the plant body according to the present invention comprises at least the above transformation step. Furthermore, the method may also comprise a step of constructing DNA for transformation using the above recombinant expression vector and may further comprise other steps. Specifically, an example of such steps is a selection step of selecting an appropriate transformant from transformed plant bodies.

A selection method is not particularly limited. For example, selection can be carried out based on drug resistance such as hygromycin resistance. Selection can also be carried out based on dry weights of plant bodies themselves or dry weights of arbitrary organs or tissues after transformants are grown. For example, an example of a selection method based on dry weights is a method that involves collecting the above-ground parts of plant bodies, performing dry treatment under predetermined conditions, measuring the weights, and then comparing the weights with the dry weights of the above-ground parts of untransformed plant bodies (see Examples described later).

In the method for producing the plant body according to the present invention, the above fusion gene is introduced into plant bodies, so as to make it possible to obtain, from the plant bodies, progeny with significantly improved fat and oil contents through sexual reproduction or asexual reproduction. Also, it becomes possible to obtain, from the plant bodies or the progeny thereof, plant cells and propagation materials such as seeds, fruits, stocks, tubers, cuttings, and masses so as to mass-produce the plant bodies based on them. Therefore, the method for producing the plant body according to the present invention may comprise a propagation step (mass-production step) for propagation of plant bodies after selection.

In addition, examples of the plant body of the present invention include at least any one of grown individual plants, plant cells, plant tissues, calli, and seeds. Specifically, in the present invention, they are all regarded as plant bodies, as long as they are in a state such that they can be finally grown to individual plants. Also, examples of the above plant cells include plant cells of various forms. Examples of such plant cells include suspension-cultured cells, protoplasts, and leaf sections. Plant bodies can be obtained by growing and causing differentiation of these plant cells. In addition, regeneration of plant bodies from plant cells can be carried out by a conventionally known method depending on the type of plant cell. Therefore, the method for producing the plant body according to the present invention may comprise a regeneration step for regenerating plant bodies from plant cells or the like.

Also, the method for producing the plant body according to the present invention is not limited to a method that involves transformation using a recombinant expression vector, and other methods may also be employed. Specifically, for example, the above chimeric protein (fusion protein) may be directly administered to plant bodies. In this case, a chimeric protein (fusion protein) is administered to plant bodies in their early life, so that fat and oil contents can be improved at sites of plant bodies that are finally used. Moreover, a method for administration of a chimeric protein (fusion protein) is also not particularly limited, and various known methods may be employed for such purpose.

As explained above, according to the present invention, through expression of a chimeric protein of a predetermined transcriptional factor and the above functional peptide, plant bodies can be provided, wherein plant weights (that is, biomass levels) are improved and substance productivity per individual plant is changed (improved or decreased) compared with that of wild-type plant bodies. When the above chimeric protein is expressed by plant bodies, the activity for accelerating transcription of a target transcriptional factor may be suppressed or transcriptional repression effects may be exerted on the homologous sequence of a cis sequence that is recognized by the target transcriptional factor. Furthermore, the chimeric protein may act to alter the affinity specificity of another factor, DNA, RNA, lipid, or carbohydrate that has affinity for the target transcriptional factor or transcription coupling factor. Alternatively, the chimeric protein may act to improve the affinity of a substance that has no affinity for the target transcriptional factor. In the plant body according to the present invention, a target transcriptional factor of a chimeric protein, a transcriptional factor that recognizes a cis sequence having homology with a cis sequence to be recognized by the target transcriptional factor, a transcriptional factor having homology with the target transcriptional factor of the chimeric protein, other factors having affinity for the target transcriptional factor of the chimeric protein, and the like are similarly expressed. However, gene expression to be controlled can be suppressed dominant-negatively because of the above-described action and effects of the chimeric protein. Accordingly, it is thought that in the plant body according to the present invention, the expression level of a gene group involved in plant growth as well as the expression level of a gene group involved in fat and oil production and/or decomposition of the produced fats and oils are changed, as a result, the biomass levels are significantly improved and fat and oil contents are significantly changed.

Here, the expression, “fat and oil contents are significantly changed” refers to a case in which fat and oil levels are improved although the seed mass per grain remains unchanged compared with that of wild-type plants; a case in which fat and oil levels are improved while the seed mass per grain is significantly increased or decreased compared with that of wild-type plants; or a case in which fat and oil contents in seeds are improved or decreased compared with those of wild-type plants. In any case, the level of fats and oils produced by an individual plant is changed.

More specifically, when a chimeric protein of the transcriptional factor At3g04070 or the transcriptional factor At1g18330 is expressed, the biomass level in the plant body is increased, but the fat and oil content is decreased. In contrast, when a chimeric protein of the transcriptional factor At3g45150 is expressed, both the biomass level and the fat and oil content are increased.

Among examples of the plant body according to the present invention, plant bodies in which fat and oil contents are increased can be used for a method for producing plant-derived fats and oils. For example, fats and oils can be produced by growing the plant body according to the present invention, harvesting seeds, and then collecting fat and oil components from the harvested seeds. Particularly, a method for producing fats and oils using the plant body according to the present invention can be said to be excellent in productivity because the fat and oil content of the thus produced individual plant is high. That is to say, if it is assumed that the number of cultivated plants per unit of cultivated area stays constant, the fat and oil level produced per unit of cultivated area can be significantly improved through the use of the plant body according to the present invention. Therefore, the use of the plant body according to the present invention makes it possible to significantly reduce the production costs of fats and oils.

Furthermore, a method for producing fats and oils using the plant body according to the present invention can be said to be excellent in productivity because of resulting high fat and oil contents in seeds per unit of weight.

In addition, examples of fats and oils to be produced by the method for producing fats and oils using the plant body according to the present invention are not particularly limited and include plant-derived fats and oils such as soybean oil, sesame oil, olive oil, coconut oil, rice oil, cottonseed oil, sunflower oil, corn oil, safflower oil, and rapeseed oil. Moreover, the thus produced fats and oils can be broadly used for household and industrial applications. The fats and oils can further be used as raw materials for biodiesel fuel. Specifically, through the use of plant bodies according to the present invention, the above-mentioned fats and oils for household or industrial applications, biodiesel fuel, or the like can be produced at low cost.

In addition, among examples of the plant body according to the present invention, plant bodies with decreased fat and oil contents can be used for a method for producing bioalcohol using lignocellulose contained in plants. Specifically, bioalcohol with excellent glycosylation efficiency and low impurity content can be produced due to the low levels of fat and oil components (which are impurities) in the step of glycosylating lignocellulose.

EXAMPLES

The present invention will be described in detail using examples as follows, but the technical scope of the present invention is not limited by these examples.

Example 1 Amplification of Transcriptional Factor Gene

A DNA fragment of the coding region of transcriptional factor At3g04070 excluding the termination codon was amplified by PCR using primers described below from an Arabidopsis thaliana cDNA library. PCR was performed in 25 cycles each consisting of 94 degrees C. for 1 minute, 47 degrees C. for 2 minutes and an extension reaction at 74 degrees C. for 1 minute. Next, PCR products were separated and collected by agarose gel electrophoresis.

Forward primer 1 (SEQ ID NO: 7) GATGATAAGCAAGGATCCAAGATCGAGTTT Reverse primer 1 (SEQ ID NO: 8) GCCTTGATATTGAAGGTGAGAACTCATCAT Preparation of Modified Transcriptional Factor

A p35SSXG vector having an Sma I site and a repressor domain (amino acid sequence: GLDLDLELRLGFA (SEQ ID NO: 9)) sequence downstream of a CaMV35S promoter was used to add a repressor domain sequence to the 3′ end of the transcriptional factor gene encoded by the DNA fragment. To link the transcriptional factor gene sequence and the repressor domain sequence, the vector was digested with Sma I and then the PCR amplified fragment encoding the above transcriptional factor was inserted. Thus, p35SSXG (At3g04070) was prepared.

Construction of Modified Transcriptional Factor Expression Vector

For gene transfer into plants using Agrobacterium, pBCKH was used as a binary vector. This vector was constructed by incorporating a Gateway vector conversion system cassette (Invitrogen) into the Hind III site of pBIG (Hygr) (Nucleic Acids Res. 18, 203 (1990)). To incorporate the modified transcriptional factor gene sequence into the vector, the vector and p35SSXG (At3g04070) were mixed and then a recombination reaction was carried out using GATEWAY LR clonase (Invitrogen). Thus, pBCKH-p35SSXG (At3g04070) was constructed.

Introduction of Modified Transcriptional Factor Gene Expression Vector into Plant

Arabidopsis thaliana (Columbia (Col-0)) was used as a plant for introduction of the modified transcriptional factor. Gene transfer was carried out according to Transformation of Arabidopsis thaliana by Vacuum Infiltration (http://www.bch.msu.edu/pamgreen/protocol.htm). However, plants were only infected by immersing them in an Agrobacterium solution without performing decompression treatment. Specifically, the modified transcriptional factor expression vector pBCKH-p35SSXG (At3g04070) was introduced into soil bacterium Agrobacterium tumefaciens strain GV3101 (C58C1Rifr) pMP90 (Gmr) (koncz, and Schell 1986) strain by electroporation. The thus introduced bacteria were cultured in 1 liter of YEP medium containing an antibiotic (kanamycin (Km): 50 microgram/ml; gentamicin (Gm); 25 microgram/ml; rifampicin (Rif): 50 microgram/ml) until OD600 reached 1. Subsequently, bacteria were collected from the culture solution and then suspended in 1 liter of medium for infection (infiltration medium containing 2.2 g of MS salt, 1× B5 vitamins, 50 g of sucrose, 0.5 g of MES, 0.044 micro M benzylaminopurine, and 400 microliter of Silwet per liter; pH 5.7).

Arabidopsis thaliana plants grown for 14 days were immersed in the solution for 1 minute for infection. After infection, cultivation was continued to fructification. Harvested seeds (T1 seeds) were sterilized in 50% bleach with 0.02% Triton X-100 solution for 7 minutes, rinsed 3 times with sterile water, and then germinated on a sterilized hygromycin selective medium (4.3 g/l MS salts, 0.5% sucrose, 0.5 g/l MES, pH 5.7, 0.8% agar, 30 mg/l hygromycin, and 250 mg/l Vancomycin). Ten (10) lines of transformed plant bodies (T1 plants) that had grown on the above hygromycin selective medium were selected per modified transcription gene. Plants were then transplanted into pots with a diameter of 50 mm containing vermiculite mixed with soil. They were cultivated at 22 degrees C. under 16-hour-light/8-hour-dark photoperiods and light intensity ranging from approximately 60 to 80 micro mol m⁻² s⁻¹. Thus, seeds (T2 seeds) were obtained.

Analysis of T2 Seed

Ten (10) lines into which At3g04070-SRDX had been introduced were each analyzed. Fat and oil contents were measured for T1 generation plants and T2 seeds.

Quantitative analysis of fats and oils was conducted using MARAN-23 (Resonance Instruments Ltd., UK) H-NMR and analysis software RI-NMR Ver. 2.0, so that 2 mg to 10 mg of Arabidopsis thaliana seeds were measured. A calibration curve was produced using olive oil as a standard substance for fats and oils. Thus, fat and oil contents (% by weight) in seeds were found.

The results of analyzing T2 seeds of the 10 lines produced for the At3g04070-SRDX gene are summarized in Table 1. The seed fat and oil content of control WT into which no gene had been introduced was 34.9+/−3.8%. The fat and oil contents of lines into which the modified transcriptional factor gene had been introduced were 19.5% at minimum and 29.4% at maximum.

TABLE 1 Line name Fat and oil content At3g04070SRDX-1 19.5% At3g04070SRDX-2 19.9% At3g04070SRDX-3 23.3% At3g04070SRDX-4 27.4% At3g04070SRDX-5 26.8% At3g04070SRDX-6 28.0% At3g04070SRDX-7 28.6% At3g04070SRDX-8 29.4% At3g04070SRDX-9 25.5% At3g04070SRDX-10 24.1% WT(n = 34) 34.9 ± 3.8% Analysis of Biomass

T2 seeds of 2 lines out of 10 lines into which the At3g04070-SRDX gene had been introduced were germinated and then cultivated. The biomass level per individual plant was measured.

First, T2 plants were cultivated for analysis of T3 plant bodies. T2 seeds were sterilized in 50% bleach with 0.02% Triton X-100 solution for 7 minutes, rinsed 3 times with sterile water, and then germinated on sterilized medium for germination (4.3 g/l MS salts, 0.5% sucrose, pH 5.7, 0.8% agar, and 10 mg/l hygromycin). Three (3) weeks after germination, the thus grown individual plants into which the gene had been introduced (specifically, 5 to 6 transformed plant bodies (T2 plants) per line) were transplanted into pots with a diameter of 50 mm containing vermiculite mixed with soil. As control plants, four non-recombinant Arabidopsis thaliana plants were transplanted. They were further cultivated at 22 degrees C. under 16-hour-light/8-hour-dark photoperiods and light intensity ranging from approximately 30 to 45 micro mol m⁻² s⁻¹ for 11 weeks.

Above-the-ground plant bodies were put into paper bags and then dried under conditions of 22 degrees C. and humidity of 60% for 2 weeks. Total biomass weight levels were then determined. The results are shown in Table 2.

TABLE 2 Biomass weight Percentage Biomass weight increase in Sample name (mg) biomass At3g04070SRDX-1-1 915.5 4.0% At3g04070SRDX-1-2 978.6 11.1% At3g04070SRDX-1-3 936.2 6.3% At3g04070SRDX-1-4 1048.0 19.0% At3g04070SRDX-1-5 910.0 3.3% At3g04070SRDX-1-6 946.9 7.5% average 955.9 8.6% At3g04070SRDX-2-1 1019.7 15.8% At3g04070SRDX-2-2 1037.2 17.8% At3g04070SRDX-2-3 1016.6 15.4% At3g04070SRDX-2-4 987.7 12.2% At3g04070SRDX-2-5 1027.2 16.6% average 1017.7 15.6% WT1 903.4 — WT2 880.3 — WT3 911.1 — WT4 827.6 — average 880.6 —

As a result, the biomass level per individual plant of the line into which the At3g04070-SRDX gene had been introduced was increased by 19% at maximum compared with that of the wild-type plants. Also, the biomass levels of the two lines were increased by 8.6% and 15.6%, respectively, on average. Hence, the biomass production per individual plant could be increased through introduction of the above modified transcriptional factor gene At3g04070-SRDX into which the repressor domain had been added. In addition, regarding At3g04070, functions relating to biomass have never before been reported.

Example 2 Amplification of Transcriptional Factor Gene

A DNA fragment of the coding region of transcriptional factor At1g18330 excluding the termination codon was amplified by PCR using primers described below from Arabidopsis thaliana cDNA library. PCR was performed in 25 cycles each consisting of 94 degrees C. for 1 minute, 47 degrees C. for 2 minutes, and an extension reaction at 74 degrees C. for 1 minute. Next, PCR products were separated and collected by agarose gel electrophoresis.

Forward primer 1 (SEQ ID NO: 10) GATGGCCGCTGAGGATCGAAGTGAGGAACT Reverse primer 1 (SEQ ID NO: 11) GCATATACGTGCTCTTTGGCTTTTCTTTTC Preparation of Modified Transcriptional Factor

A p35SSXG vector having an Sma I site and a repressor domain (amino acid sequence: GLDLDLELRLGFA (SEQ ID NO: 9)) sequence downstream of a CaMV35S promoter was used to add a repressor domain sequence to the 3′ end of the transcriptional factor gene encoded by the DNA fragment. To link the transcriptional factor gene sequence and the repressor domain sequence, the vector was digested with Sma I and then the PCR amplified fragment encoding the above transcriptional factor was inserted. Thus, p35SSXG (At1g18330) was prepared.

Construction of Modified Transcriptional Factor Expression Vector

For gene transfer using Agrobacterium into plants, pBCKH was used as a binary vector. This vector was constructed by incorporating a cassette of a Gateway vector conversion system (Invitrogen) into a Hind III site of pBIG (Hygr) (Nucleic Acids Res. 18, 203 (1990)). To incorporate the modified transcriptional factor gene sequence into the vector, the vector and p35SSXG (At1g18330) were mixed and then a recombination reaction was carried out using GATEWAY LR clonase (Invitrogen). Thus, pBCKH-p35SSXG (At1g18330) was constructed.

Introduction of Modified Transcriptional Factor Gene Expression Vector into Plant

Arabidopsis thaliana (Columbia (Col-0)) was used as a plant for introduction of the modified transcriptional factor. Gene transfer was carried out according to Transformation of Arabidopsis thaliana by Vacuum Infiltration (http://www.bch.msu.edu/pamgreen/protocol.htm). However, plants were only infected by immersing them in an Agrobacterium solution without performing decompression treatment. Specifically, the modified transcriptional factor expression vector pBCKH-p35SSXG (At1g18330) was introduced into soil bacterium Agrobacterium tumefaciens strain GV3101 (C58C1Rifr) pMP90 (Gmr) (koncz and Schell 1986) strain by electroporation. The thus introduced bacteria were cultured in 1 liter of YEP medium containing an antibiotic (kanamycin (Km) 50 microgram/ml, gentamicin (Gm) 25 microgram/ml, and rifampicin (Rif) 50 microgram/ml) until OD600 reached 1. Subsequently, bacteria were collected from the culture solution and then suspended in 1 liter of medium for infection (Infiltration medium containing 2.2 g of MS salt, 1× B5 vitamins, 50 g of sucrose, 0.5 g of MES, 0.044 micro M benzylaminopurine, and 400 microliter of Silwet per liter; pH 5.7).

Arabidopsis thaliana plants grown for 14 days were immersed in the solution for 1 minute for infection. After infection, cultivation was continued to fructification. Harvested seeds (T1 seeds) were sterilized in 50% bleach with 0.02% Triton X-100 solution for 7 minutes, rinsed 3 times with sterile water, and then germinated on sterilized hygromycin selective medium (4.3 g/l MS salts, 0.5% sucrose, 0.5 g/l MES, pH 5.7, 0.8% agar, 30 mg/l hygromycin, and 250 mg/l Vancomycin). Ten (10) lines of transformed plant bodies (T1 plants) that had grown on the above hygromycin selective medium were selected per modified transcription gene. Plants were then transplanted into pots with a diameter of 50 mm containing vermiculite mixed with soil. They were cultivated at 22 degrees C. under 16-hour-light/8-hour-dark photoperiods and light intensity ranging from approximately 60 to 80 micro mol m⁻² s⁻¹. Thus, seeds (T2 seeds) were obtained.

Analysis of T2 Seed

Ten (10) lines into which At1g18330-SRDX had been introduced were each analyzed. Fat and oil contents were measured for T1 generation plants and T2 seeds. Quantitative analysis of fats and oils was conducted using MARAN-23 (Resonance Instruments Ltd., UK) H-NMR and analysis software RI-NMR Ver. 2.0, so that 2 mg to 10 mg of Arabidopsis thaliana seeds were measured. A calibration curve was produced using olive oil as a standard substance for fats and oils. Thus, fat and oil contents (% by weight) in seeds were found.

The results of analyzing T2 seeds of the 10 lines produced for the At1g18330-SRDX gene are summarized in Table 3. The seed fat and oil content of control WT into which no gene had been introduced was 34.9+/−3.8%. The fat and oil contents of lines into which the modified transcriptional factor gene had been introduced were 22.0% at minimum and 33.7% at maximum.

TABLE 3 Percentage Gene name Lipid level decrease At1g18330-1 33.7% −3.6% At1g18330-2 30.2% −13.5% At1g18330-3 30.6% −12.3% At1g18330-4 24.7% −29.3% At1g18330-5 26.2% −24.9% At1g18330-6 26.5% −24.2% At1g18330-7 22.8% −34.6% At1g18330-8 22.0% −37.0% At1g18330-9 26.9% −23.0% At1g18330-10 32.8% −5.9% WT(n = 34) 34.9 ± 3.8% Analysis of Biomass

T2 seeds of 1 line out of the 10 lines into which the At1g18330-SRDX gene had been introduced were germinated and then cultivated. The biomass level per individual plant was measured. First, T2 plants were cultivated for analysis of T3 plant bodies. T2 seeds were sterilized in 50% bleach with 0.02% Triton X-100 solution for 7 minutes, rinsed 3 times with sterile water, and then germinated on sterilized medium for germination (4.3 g/l MS salts, 0.5% sucrose, pH 5.7, 0.8% agar, and 10 mg/l hygromycin). Three (3) weeks after germination, the thus grown individual plants into which the gene had been introduced (specifically, 4 transformed plant bodies (T2 plants)) were transplanted into pots with a diameter of 50 mm containing vermiculite mixed with soil. As control plants, four non-recombinant Arabidopsis thaliana plants were transplanted. They were further cultivated at 22 degrees C. under 16-hour-light/8-hour-dark photoperiods and light intensity ranging from approximately 30 to 45 micro mol m⁻² s⁻¹ for 11 weeks.

Above-the-ground plant bodies were put into paper bags and then dried under conditions of 22 degrees C. and humidity of 60% for 2 weeks. Total biomass weight levels were then determined. The results are shown in Table 4.

TABLE 4 Percentage Biomass weight increase in Sample name (mg) biomass At1g18330SRDX-5-1 978.8 13.9% At1g18330SRDX-5-2 1202.5 39.9% At1g18330SRDX-5-3 1015.9 18.2% At1g18330SRDX-5-4 884.8 3.0% average 1020.5 18.8% WT1 698.0 — WT2 958.6 — WT3 884.1 — WT4 896.2 — average 859.2 —

As a result, the biomass level per individual plant of the line into which the At1g18330-SRDX gene had been introduced was increased by 39.9% at maximum compared with that of the wild-type plants. Also, the biomass level per individual plant of each line was increased by 18.8%, on average. Hence, the biomass production per individual plant could be increased through introduction of the above modified transcriptional factor gene At1g18330-SRDX into which the repressor domain had been added. In addition, regarding At1g18330, there is a report that flowering is delayed by functional deficiency, but there is no report that it relates to biomass.

Example 3 Amplification of Transcriptional Factor Gene

A DNA fragment of the coding region of transcriptional factor At3g45150 excluding the termination codon was amplified by PCR using primers described below from Arabidopsis thaliana cDNA library. PCR was performed in 25 cycles each consisting of 94 degrees C. for 1 minute, 47 degrees C. for 2 minutes, and an extension reaction at 74 degrees C. for 1 minute. Next, PCR products were separated and collected by agarose gel electrophoresis.

Forward primer 1 (SEQ ID NO: 12) ATGGATTCGAAAAATGGAATTAAC Reverse primer 1 (SEQ ID NO: 13) AACTGTGGTTGTGGCTGTTGTTG Preparation of Modified Transcriptional Factor

A p35SSXG vector having an Sma I site and a repressor domain (amino acid sequence: GLDLDLELRLGFA (SEQ ID NO: 9)) sequence downstream of a CaMV35S promoter was used to add a repressor domain sequence to the 3′ end of the transcriptional factor gene encoded by the DNA fragment. To link the transcriptional factor gene sequence and the repressor domain sequence, the vector was digested with Sma I and then the PCR amplified fragment encoding the above transcriptional factor was inserted. Thus, p35SSXG (At3g45150) was prepared.

Construction of Modified Transcriptional Factor Expression Vector

For gene transfer using Agrobacterium into plants, pBCKH was used as a binary vector. This vector was constructed by incorporating a cassette of a Gateway vector conversion system (Invitrogen) into a Hind III site of pBIG (Hygr) (Nucleic Acids Res. 18, 203 (1990)). To incorporate the modified transcriptional factor gene sequence into the vector, the vector and p35SSXG (At3g45150) were mixed and then a recombination reaction was carried out using GATEWAY LR clonase (Invitrogen). Thus, pBCKH-p35SSXG (At3g45150) was constructed.

Introduction of Modified Transcriptional Factor Gene Expression Vector into Plant

Arabidopsis thaliana (Columbia (Col-0)) was used as a plant for introduction of the modified transcriptional factor. Gene transfer was carried out according to Transformation of Arabidopsis thaliana by Vacuum Infiltration (http://www.bch.msu.edu/pamgreen/protocol.htm). However, plants were only infected by immersing them in an Agrobacterium solution without performing decompression treatment. Specifically, the modified transcriptional factor expression vector pBCKH-p35SSXG (At3g45150) was introduced into soil bacterium Agrobacterium tumefaciens strain GV3101 (C58C1Rifr) pMP90 (Gmr) (koncz and Schell 1986) strain by electroporation. The thus introduced bacteria were cultured in 1 liter of YEP medium containing an antibiotic (kanamycin (Km) 50 microgram/ml, gentamicin (Gm) 25 microgram/ml, and rifampicin (Rif) 50 microgram/ml) until OD600 reached 1. Subsequently, bacteria were collected from the culture solution and then suspended in 1 liter of medium for infection (Infiltration medium containing 2.2 g of MS salt, 1× B5 vitamins, 50 g of sucrose, 0.5 g of MES, 0.044 micro M benzylaminopurine, and 400 microliter of Silwet per liter; pH 5.7).

Arabidopsis thaliana plants grown for 14 days were immersed in the solution for 1 minute for infection. After infection, cultivation was continued to fructification. Harvested seeds (T1 seeds) were sterilized in 50% bleach with 0.02% Triton X-100 solution for 7 minutes, rinsed 3 times with sterile water, and then germinated on sterilized hygromycin selective medium (4.3 g/l MS salts, 0.5% sucrose, 0.5 g/l MES, pH 5.7, 0.8% agar, 30 mg/l hygromycin, and 250 mg/l Vancomycin). Ten (10) lines of transformed plant bodies (T1 plants) that had grown on the above hygromycin selective medium were selected per modified transcription gene. Plants were then transplanted into pots with a diameter of 50 mm containing vermiculite mixed with soil. They were cultivated at 22 degrees C. under 16-hour-light/8-hour-dark photoperiods and light intensity ranging from approximately 60 to 80 micro mol m⁻² s⁻¹. Thus, seeds (T2 seeds) were obtained.

Analysis of Fat and Oil Content in T2 Seed

Ten (10) lines into which At3g45150-SRDX had been introduced were each analyzed. Fat and oil contents were measured for T1 generation plants and T2 seeds. Quantitative analysis of fats and oils was conducted using MARAN-23 (Resonance Instruments Ltd., UK) H-NMR and analysis software RI-NMR Ver. 2.0, so that 2 mg to 10 mg of Arabidopsis thaliana seeds were measured. A calibration curve was produced using olive oil as a standard substance for fats and oils. Thus, fat and oil contents (% by weight) in seeds were found.

As a result of analyzing T2 seeds of the 10 lines produced for the At3g45150-SRDX gene, the fat and oil contents in T2 seeds of the 10 lines were 46.4%, 40.7%, 40.0%, 35.7%, 35.4%, 34.8%, 33.6%, 31.1%, 30.6%, and 26.7% (46.4% at maximum and 26.7% at minimum). The seed fat and oil content of control WT into which no gene had been introduced was 34.9+/−3.8%. From these lines, the line with the fat and oil content of 40.7% was used for the subsequent experiments.

Cultivation Test and Analysis of Biomass and Fat and Oil Content

T2 seeds of 1 line out of the 10 lines into which the At3g45150-SRDX gene had been introduced were germinated and then cultivated. The biomass level per individual plant was measured. First, T2 plants were cultivated for analysis of T3 plant bodies. T2 seeds were sterilized in 50% bleach with 0.02% Triton X-100 solution for 7 minutes, rinsed 3 times with sterile water, and then germinated on sterilized medium for germination (4.3 g/l MS salts, 0.5% sucrose, pH 5.7, 0.8% agar, and 10 mg/l hygromycin). Three (3) weeks after germination, the thus grown individual plants into which the gene had been introduced (specifically, 5 transformed plant bodies (T2 plants)) were transplanted into pots with a diameter of 50 mm containing vermiculite mixed with soil. As control plants, four non-recombinant Arabidopsis thaliana plants were transplanted. They were further cultivated at 22 degrees C. under 16-hour-light/8-hour-dark photoperiods and light intensity ranging from approximately 30 to 45 micro mol m⁻² s⁻¹ for 11 weeks.

Above-the-ground plant bodies were put into paper bags and then dried under conditions of 22 degrees C. and humidity of 60% for 2 weeks. Total biomass weight levels were then determined and the above fat and oil contents were measured. The results are shown in Table 5.

TABLE 5 Biomass Percentage Fat and oil Percentage weight increase in content in increase in Sample name (mg) biomass seed fats and oils At3g45150SRDX-27-1 893.7 25.9% 36.0% 3.1% At3g45150SRDX-27-2 875.3 23.3% 36.6% 4.9% At3g45150SRDX-27-3 1115.7 57.2% 37.1% 6.5% At3g45150SRDX-27-5 820.1 15.6% 35.1% 0.7% At3g45150SRDX-27-6 827.7 16.6% 35.9% 3.0% average 906.5 27.7% 36.1% 3.7% WT1 818.7 — 35.3% — WT2 784.5 — 34.8% — WT3 627.5 — 35.2% — WT4 608.0 — 34.1% — average 709.6 — 34.9% —

As a result, the biomass level per individual plant of the line into which the At3g45150-SRDX gene had been introduced was increased by 57.2% at maximum compared with that of the wild-type plants. The biomass level per individual plant of each line was increased by 27.7% on average. Also, when the fat and oil contents in dry seeds were measured by pulse NMR, they were confirmed to be improved by 6.5% at maximum and 3.7% on average. Hence, the biomass production per individual plant could be increased through introduction of the above modified transcriptional factor gene At3g45150-SRDX into which the repressor domain had been added. In addition, regarding At3g45150, there is a report that functional deficiency induces underdevelopment of pollens, but there is no report that this matter relates to biomass. 

The invention claimed is:
 1. A method for producing a plant exhibiting an improved biomass level and having an improved productivity of a substance per individual plant compared with a wild type plant, comprising the steps of: introducing a fusion gene into a plant, wherein the fusion gene codes for a chimeric protein comprising a transcriptional factor comprising any one of the following proteins (a) to (b) and a functional peptide that converts an arbitrary transcriptional factor into a transcriptional repression factor: (a) a protein comprising the amino acid sequence shown in SEQ ID NO: 4; and (b) a protein comprising the amino acid sequence of SEQ ID NO: 4 but with 1-20 amino acid changes, wherein said amino acid changes are selected from the group consisting of a deletion, a substitution, an addition, and an insertion, and wherein the protein has an activity of accelerating transcription, and selecting a plant having the introduced fusion gene, exhibiting an improved biomass level and having an improved productivity of a substance compared with a wild type plant.
 2. The method according to claim 1, wherein the activity of accelerating transcription of the transcriptional factor is suppressed.
 3. The method according to claim 1, wherein the chimeric protein has transcriptional repression factor activity.
 4. The method according to claim 1, wherein the functional peptide has the amino acid sequence represented by any one of the following formulae (1) to (8): X1-Leu-Asp-Leu-X2-Leu-X3 (SEQ ID NO: 14 with deletion of 0-10 residues from the N-terminus)  (1) (wherein X1 denotes 0 to 10 amino acid residues, X2 denotes Asn or Glu, and X3 denotes at least 6 amino acid residues); Y1-Phe-Asp-Leu-Asn-Y2-Y3 (SEQ ID NO: 15 with deletion of 0-10 residues from the N-terminus)  (2) (wherein Y1 denotes 0 to 10 amino acid residues, Y2 denotes Phe or Ile, and Y3 denotes at least 6 amino acid residues); Z1-Asp-Leu-Z2-Leu-Arg-Leu-Z3 (SEQ ID NO: 16 with deletion of 0-10 residues from the C-terminus and deletion of 0-2 residues from the N-terminus)  (3) (wherein Z1 denotes Leu, Asp-Leu, or Leu-Asp-Leu, Z2 denotes Glu, Gln, or Asp, and Z3 denotes 0 to 10 amino acid residues); Asp-Leu-Z4-Leu-Arg-Leu (SEQ ID NO: 17)  (4) (wherein Z4 denotes Glu, Gln, or Asp); α1-Leu-β1-Leu-γ1-Leu (SEQ ID NO: 18);  (5) α1-Leu-β1-Leu-γ2-Leu (SEQ ID NO: 19);  (6) α1-Leu-β1-Leu-Arg-Leu (SEQ ID NO: 20); and  (7) α2-Leu-β1-Leu-Arg-Leu (SEQ ID NO: 21)  (8) (and in the formulae (5) to (8), α1 denotes Asp, Asn, Glu, Gln, Thr, or Ser, α2 denotes Asn, Glu, Gln, Thr, or Ser, β1 denotes Asp, Gln, Asn, Arg, Glu, Thr, Ser, or His, β2 denotes Asn, Arg, Thr, Ser, or His, γ1 denotes Arg, Gln, Asn, Thr, Ser, His, Lys, or Asp, and γ2 denotes Gln, Asn, Thr, Ser, His, Lys, or Asp).
 5. The method according to claim 1, wherein the plant weight is significantly improved.
 6. The method according to claim 1, wherein the substance productivity per individual plant is productivity of fats and oils contained in seeds.
 7. The method according to claim 1, wherein the plant is an angiosperm.
 8. The method according to claim 1, wherein the plant is a dicotyledon.
 9. The method according to claim 1, wherein the plant is a plant of the family Brassicaceae.
 10. The method according to claim 1, wherein the plant is Arabidopsis thaliana. 